On-board capacity estimation of lithium iron phosphate batteries by means of half-cell curves

Significance Statement

Battery management systems face usually different challenging tasks. One of the most important concerns the on-board evaluation of the total battery capacity in electric and hybrid electric vehicles. This is due to the fact that the battery capacity has to be computed without necessarily discharging the battery entirely starting from a fully charged state. In fact, during the vehicle operations, the discharge process is mainly carried out in a dynamic condition under variable current rates and temperature. Selecting a method to be used in this process has poised a challenge mainly for lithium iron phosphate cells.

In a recent paper published in Journal of Power Sources, Andrea Marongiu and colleagues estimated lithium iron phosphate batteries capacity by means of half-cell curves. Their research mainly focused on developing a new approach that is based on the detection of the actual degradation mechanisms by collecting plateau information.

First, a model was developed and introduced which described the characteristics of the electrode voltage curves of the lithium iron phosphate cells and the impact of aging on the full cell voltage. A description of the main degradation mechanisms that can occur during the lifetime of the lithium iron phosphate cell and a model capable of describing the effects of degradation on the electrode and on the full cell voltage curves were presented. The research team then introduced a new battery management system structure with an implemented algorithm for on-board capacity estimation.

The results reported in the work show that not all the information from the voltage plateaus has to be collected at the same time although the collection phases have to be over short duration intervals. The new introduced algorithm is simple to parametrize, since only the characteristics of the cell in a fresh state are needed, in terms of stoichiometry and half-cell voltage curves. Eventually, both during charge and discharge the algorithm is able to correctly track the actual battery capacity with an error of approximately 1%. Also, the new proposed BMS structure is designed in a way that part of the novel methodology can run offline (not-real time). This means that the approach can be implemented in cheap microcontrollers, as it does not need to be executed in real time.

The method presented in this paper is valid for lithium iron phosphate /G cells, primarily due to the need of collecting data of plateaus, which is one of the main features of this type of cells. Nevertheless, the proposed model and the approach shown in the literature have a general formulation, which demonstrate the benefit of the tracked aging information for different lithium-ion technologies and additional application scopes.

On-board capacity estimation of lithium iron phosphate batteries by means of half-cell curves - renewable global energy innovations

About The Author

Andrea Marongiu received his master degree in Electrical Engineering from the Cagliari University, Italy, in 2010. In March 2011 he joined the Institute for Power Electronics and Electrical Drives (ISEA) at the RWTH Aachen University, Germany, as a research associate and PhD student.

His areas of interest were lithium-ion batteries with special focus on lithium iron phosphate-based cells, EV batteries and the related on board Battery Management System. From August 2016 to February 2017 he worked as Lead Engineer Battery Algorithm at National Electric Vehicle Sweden AB in Sweden. Since March 2017 he works as battery expert at IK4-CIDETEC in Spain, in the field of hybrid system for automotive applications.

About The Author

Dirk Uwe Sauer currently holds the title of professor for electrochemical energy conversion and storage systems at the Institute for Power Electronics and Electrical Drives (ISEA) & Institute for Power Generation and Storage Systems (PGS) at E.ON ERC RWTH Aachen University as well as Principle Investigator at Helmholtz Institute Münster Ionics in Energy Storage.

Originally, professor Sauer studied physics at University of Darmstadt, Germany, and upon graduating in 1994 became a scientist, project coordinator and head of group at Fraunhofer Institute for Solar Energy Systems ISE in Freiburg until 2003. While at the Fraunhofer Institute for Solar Energy Systems ISE, Professor Sauer headed the groups for storage systems, the interdisciplinary team for off-grid and remote power supply-systems, and was the managing director of the club for rural electrification. In 2003, he was appointed as junior professor at RWTH Aachen University, in 2009 he was appointed as professor, and in 2012 he was appointed as full professor for electrochemical energy conversion and storage systems at RWTH Aachen University. In 2010, he became a founding partner of P3 Energy & Storage, and in 2015 he became a founding partner of both BatterieIngenieure GmbH as well as eBusplan GmbH. Together with Prof. Martin Winter he is chairman of the conference “Kraftwerk Batterie / Advanced Battery Power”.

About The Author

Nsombo Nlandi has studied computer science at the RWTH Aachen University in Germany and received his master degree in 2009. In 2013 he got his second master degree in electrical engineering at the University of Hagen, Germany. From 2009 to 2016 he worked as researcher associate at the Institute for Power Electronics and Electrical Drives (ISEA), where he pursued his PhD. His research interests were mainly focused on software for battery diagnostic, namely the development of intelligent Battery Management Systems (BMS). Since August 2016 he has joined National Electric Vehicle Sweden AB (Sweden) as Lead Engineer for Embedded Systems.

About The Author

Yao RONG was born in Nanjing, China. He received his bachelor degree in Electrical Power Engineering and Automation from the Shanghai Jiao Tong University in 2007. Afterwards he studied at the RWTH Aachen University the master course of Electrical Power Engineering. During this period he wrote his master thesis at the Institute for Power Electronics and Electrical Drives (ISEA), working meanwhile a student assistant. He obtained his master degree in 2014. In 2015 he joined Jiangsu Marathon Investment Management Co., Ltd In China, where he works currently as chief research officer.

References

Andrea Marongiu1,3, Nsombo Nlandi1,3, Yao Rong1,3, Dirk Uwe Sauer1,2,3. On-board capacity estimation of lithium iron phosphate batteries by means of half-cell curves.  Journal of Power Sources volume 324 (2016) pages 158-169.

Show Affiliations
  1. Electrochemical Energy Conversion and Storage Systems Group, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University, Jägerstrasse 17/19, D-52066 Aachen, Germany
  2. Institute for Power Generation and Storage Systems (PGS), E.ON ERC, RWTH Aachen University, Mathieustrasse, D-52074 Aachen, Germany
  3. Jülich Aachen Research Alliance, JARA-Energy, Germany

 

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